To allow use of the full nix language for my inputs, I use genflake.
Therefore, the flake I edit is located at $FLAKE/_outputs.nix.
I also prefer using a more descriptive format for my inputs like so:
nixpkgs = {
type = "github";
owner = "NixOS";
repo = "nixpkgs";
# Branch name
ref = "nixos-unstable";
# Pin this input to a specific commit
rev = "842d9d80cfd4560648c785f8a4e6f3b096790e19";
};to make it more clear what is what in the flake URI